The WWII-thingie did seem random... I had the feeling that they had been trying to figure out which time setting could be used without contradicting the other films while having the audience have a particular relation to this specific time. I mean, WWII is still a touchy subject, makes up for a 'good film set up' and provides enough drama and action to start a film with. Plus, so far, we have experienced Wolverine in a lot of different settings, and WWII seemed to be the easiest choice to continue/start with.
It appeared to be more of an arbitrary decision though - as I am not too familiar with the comic books and have seen the other films only once or twice I am part of the 'average-knowledge-audience'- so it made me wonder what on earth Wolverine was doing in Japan during WWII.
For me personally, this had the consequence that the character Wolverine seemed even more impalpable, distant, mysterious. I have never actually felt anything for the character, as in 'Do I like him now? - Do I hate him? - Sympathy? Maybe yes, maybe no...I don't know.'

Throughout the film, though, I did actually get the feeling - ah, I start to understand this guy - mainly because I started to understand his relationship to Jean.

Another thing I didn't quite enjoy: If he's mortal/violable...why didn't his claws leave bleeding gaps? Or did I miss some essential information about them?

Also, while at some point I started to have the feeling that I'm getting the grip on the character I thought that the train and heart surgery scenes were unnecessarily over the top. I love over the top-ness but I had just gotten used to the idea that we get more character explanation/development and really enjoyed to see a somehow different Wolverine and then these scenes drop by and cut the connection I'd built up to the character moments before.